The present invention relates to a recording head for an ink-jet recording apparatus to be used as an ink-jet printer or an ink-jet plotter. More specifically, the present invention relates to the arrangement of nozzle openings and the arrangement of common ink chambers (reservoirs) in an ink-jet recording head.
A recording head employed in an ink-jet recording apparatus to be used as an ink-jet printer or an ink-jet plotter pressurizes ink contained in a pressure chamber communicating with a nozzle opening to jet an ink drop through the nozzle opening. Ink drops are jetted at times specified by a dot pattern while the recording head is moving in a scanning direction (a direction of the width of a recording medium). Upon the arrival of the recording head at a terminal position with respect to a widthwise direction, a recording medium, such as a paper sheet, is moved in a feed direction (sheet feed direction), and then ink drops are jetted as the recording head is moved again in the scanning direction.
A conventional ink-jet recording head, for example, is constructed by stacking an actuator unit and a passage unit. The actuator unit has a plurality of pressure chambers arranged in a row and a plurality of pressure generators for applying pressure to inks contained in the pressure chambers. The passage unit has a plurality of nozzle openings communicating with the pressure chambers to jet ink drops when the inks contained in the pressure chambers are pressurized by the pressure generators, and common ink chambers communicating with the pressure chambers and containing the ink to be supplied into the pressure chambers.
This conventional ink-jet recording head, however, has some problems.
First, if only one kind of ink can be jetted from a plurality of pressure chambers arranged in a row, a recording head intended to jet a plurality of color inks of different colors must be provided with a plurality of pressure chambers arranged in a plurality of rows and hence the recording head inevitably has a large size.
Secondly, if a plurality of pressure chambers arranged in a row are divided in a plurality of groups of pressure chambers and the groups of pressure chambers are connected to different common ink chambers, respectively, to solve the foregoing problem, the adjacent common ink chambers must be separated from each other by relatively thick partition walls to jet the inks stably. As a result, some of the pressure chambers and some of the nozzle openings, for example, four pressure chambers and four nozzle openings, must be omitted to form the partition walls. Consequently, the number of the nozzle openings for each color group must be reduced accordingly, which makes the improvement of color print quality difficult.
Thirdly, since ink supply passages for supplying the inks from external ink sources to the common ink chambers are formed in a plane including the common ink chambers and the ink supply passages are arranged side by side, a plate provided with the common ink chambers must have a large area, which increases the width of the recording head.
The present invention has been made in view of the foregoing circumstances and it is therefore an object of the present invention to provide an ink-jet recording head capable of jetting a plurality of kinds of inks, of being formed in a small size and of attaining a high print quality.
According to the present invention, an ink-jet recording head includes an actuator unit provided with a plurality of pressure chambers arranged in a row, and a plurality of pressure generators for applying pressure to inks contained in the pressure chambers; and a passage unit provided with a plurality of nozzle openings communicating with the pressure chambers to jet ink drops when pressures are applied to the inks contained in the pressure chambers by the pressure generators, and two or more common ink chambers containing inks to be supplied to the pressure chambers. The pressure chambers arranged in a row are divided into a plurality of groups along the row, and the common ink chambers are assigned to the groups of the pressure chambers, respectively.
Preferably, the pressure chambers are formed in a single plate, the two or more common ink chambers are formed in another single plate, and the actuator unit and the passage unit are stacked together.
Preferably, each of the pressure chambers has a first end part and a second end part, the nozzle openings are connected to the first or the second end parts, the common ink chambers are connected to the second or the first end parts, the same end parts of the pressure chambers included in the same group are connected to the nozzle openings, and the end parts connected to the nozzle openings are different between one of the groups and the other group adjacent to the one of the groups.
Preferably, a first plate, a second plate, a third plate and a fourth plate are stacked successively, the first plate is provided with a plurality of pressure chamber forming holes forming the pressure chambers, respectively, the second plate is provided with a plurality of pairs of connecting holes connected to the first and the second end parts of the pressure chambers, respectively, the third plate is provided with a plurality of ink supply ports each connected to one of the connecting holes of each pair and two or more common ink chamber forming holes connected to the other one of the connecting holes of each pair and forming the two or more common ink chambers, and the fourth plate is provided with the nozzle openings.
Preferably, a fifth plate is sandwiched between the second and the third plate. The fifth plate has a thin-wall part serving as a compliance part formed in a region overlapping the common ink chamber forming hole formed in the third plate to absorb a variation of a pressure applied to the ink contained in the common ink chamber.
Preferably, at least one of the two or more common ink chambers is formed in a region overlapping a region in which the pressure chambers are formed and the other common ink chamber is formed in a region outside the region in which the pressure chambers are formed.
Preferably, the pressure generators include a plurality of piezoelectric vibrators and a plurality of terminals connected to the piezoelectric vibrators to apply voltages to the piezoelectric vibrators, and the two or more common ink chambers are formed in a region outside a region in which the terminals are formed.
Preferably, in addition to the pressure chambers arranged in a row, a plurality of pressure chambers are formed in another row parallel to the row of the pressure chambers, and a common ink chamber containing an ink to be supplied to all the pressure chambers is arranged in the another row.
Preferably, the adjacent groups of the pressure chambers are separated from each other by a partition wall of a width substantially corresponding to a width of the pressure chamber.
Preferably, the passage unit is provided further with two or more ink passages for supplying inks to the two or more common ink chambers, each of the pressure chambers has a first end part and a second end part, the nozzle openings are connected to the first end parts, the common ink chambers are connected to the second end parts, and at least one of the two or more common ink chambers is formed on a side opposite to a side on which the other common ink chamber is formed with respect to a line along which the second end parts of the pressure chambers are arranged.
Preferably, the common ink chamber formed in a region outside a region in which the pressure chambers are formed has a width decreasing in a direction away from the second end parts of the pressure chambers.
Preferably, the common ink chamber formed in the region outside the region in which the pressure chambers are formed has a downstream wall forming the common ink chamber at a position remote from an upstream end of the ink passage, the downstream wall is inclined at an angle in a range of 30xc2x0 to 45xc2x0 to the line along which the second end parts of the pressure chambers are arranged.
Preferably, the common ink chamber formed in the region outside the region in which the pressure chambers are formed has an upstream wall forming the common ink chamber at a position near an upstream end of the ink passage, the upstream wall extends substantially perpendicularly to the line along which the second end parts of the pressure chambers are arranged.
Preferably, the ink passages are formed in a plane including the common ink chambers.
Preferably, a number of the common ink chambers is at least three, at least two of the common ink chambers are formed in the region outside the region in which the pressure chambers are formed, and at least two of the ink passages connected to the at least two of the common ink chambers are formed in arcs of substantially concentric circles, respectively.
Preferably, a distance between the at least two of the ink passages connected to the at least two of the common ink chambers formed in the region outside the region in which the pressure chambers are formed is substantially constant over substantially entire lengths of the at least two of the ink passages.
Preferably, a part of the common ink chamber is formed by a thin-wall portion and a part of the ink passage is formed by a thin-wall portion near the common ink chamber.
Preferably, each of the at least two of the ink passages has a substantially uniform width over a substantially entire length thereof.
Preferably, the groups of the pressure chambers correspond to colors of the inks to be jetted through the nozzle openings, respectively.
Preferably, the pressure chambers are arranged in a plurality of rows.
In the ink-jet recording head of the foregoing construction in accordance with the present invention, the pressure chambers arranged in a row are divided into a plurality of groups, and the common ink chambers are formed respectively for the groups of pressure chambers. Therefore, a plurality of kinds of inks can be jetted and a high print quality can be attained. The ink-jet print head can be formed in a small size. Since the actuator unit provided with the pressure chambers and the passage unit provided with the common ink chambers are stacked, the design of the recording head can be easily changed.
According to the present invention, the first or the second end parts of all the pressure chambers belonging to each group are connected to the nozzles openings The first end parts of the pressure chambers belonging to the group are connected to the nozzle openings if the second end parts of the pressure chambers belonging the group adjacent to the former group are connected to the nozzle holes. Therefore, the common ink chambers do not need to be separated from each other by thick partition walls and hence only a small number of pressure chambers need to be sacrificed for the partition walls. Consequently, the number of nozzle openings for each group of pressure chambers can be increased and hence print quality can be improved.
When the groups are assigned to colors of inks, the groups of nozzles for different colors are spaced apart, the mixing of different colors that occurs during cleaning can be limited to the least extent.
According to the present invention, at least one of the two or more common ink chambers is disposed opposite to the other common ink chambers with respect to the row of the ink supply ports, the outward expansion of the common chambers is suppressed, the common chambers can be disposed in the smallest possible dead space on the plate and hence the recording head can be formed in a small width.